In using flexible colters of polyurethane or rubber, the load of the colter against the surface to be ploughed must be small, but the colter must stay in same colter angle during flexing movement. The smallness of vertical force pressing the colter is important in order to minimize wear and tear of the colter and to lengthen the life of the colter. A correct position keeps the cutting of colter edge sharp without rounding the lower surface. Rounding of colter lower surface makes the cutting edge of the coulter rise from the ground, so that snow getting under the colter lifts the colter to glide on the snow layer. The result is weakened ploughing quality.
Backing of the colter in its movement direction against a spring is known for instance from publications DE 881200, GB 1060335, GB 784049. In these publications, the colter is a plate of large size, which must always be replaced as a whole when sufficiently worn out. For the colter plate, a quite long backward directed steering box portion is arranged, which keeps the colter in the desired direction.
In using an additional colter, this colter must have same possibilities to follow the roughness of surface as the first colter.
Previously known is a suspension of a colter, where the whole plough, that is the blade and colter, is divided into transverse elements which are flexing vertically on levers or on flexible attachments. The disadvantages of this solution are the relatively heavy elements, which cause the colters to have a wearing load and hard strokes on obstacles during ploughing, because of the mass of elements. The moving of the elements gives cause to discontinuity on the blade surface and restricts the blade forming. The circle curve is almost the only possible cross-section of the blade, if the motion is dimensioned to follow the curve. The direction of the evasive movement by means of lever mechanisms is in a relatively great angle in regard to the driving motion direction and thus disadvantageous.
Previously known is also a solution where the colter is divided into separately suspended elements, which suspended elements function simply as steered by springs or separate elements, as in GB 784049. There are wearing parts in the control mechanisms. Colters resting merely on springs have too great colter forces and often insufficient control, which lead to rapid wearing and blade bottom rounding. Known is also a solution where the colter is suspended on springs of elastic rubber or of plastic.
The disadvantage of said solutions is weak control, whereby the colter wears out into a wrong form. Another disadvantage appears in speedy ploughing, and the attendant risk connected to overheating of spring material and to loss of spring material firmness due to inside frictions.
For suspension of an additional colter a further solution is known, where the additional colter is furnished with its own mechanisms both for the vertical and evasive backward motion of the colter. This is an expensive solution containing many parts.